Perineal hernia is when contents from the pelvis or abdomen is pushed between or through the pelvic diaphragm (made up of the coccygeus muscle and the levator ani muscle) into the more superficial tissues. Perineal hernias are most common in intact male dogs. Dogs may strain from a primary problem that may lead to a perineal hernia, so many times perineal hernia is a secondary diagnosis. Primary problems that may cause straining include enlarged prostate, tumors, gastrointestinal parasites, dietary indiscretion, as well as numerous other causes. It is important that when perineal hernias occur, that an investigation into the primary cause of straining is initiated.

Signs of a perineal hernia include straining to defecate, a large bulge to either side or around the anus, and possibly rectal prolapse. Perineal hernias can be diagnosed by a veterinarian on a rectal exam; they will be able to feel the defect in the pelvic diaphragm and sometimes can palpate the contents of the hernia. Any organ in the pelvic can herniate into the hernia and has the potential to become entrapped. This includes the urinary bladder, intestines, uterus, prostate, and others. Clinical signs will differ based on the contents of the henia. For example, vomiting and diarrhea may be seen if intestines are trapped. Difficulty urinating, or straining with no urine production may be noted if the bladder becomes entrapped.

Treatment of a perineal hernia includes surgery to replace the hernia contents and repair the defect in muscular diaphragm. This may include augmentation of the area using surrounding muscles, or sometimes polypropylene mesh is incorporated into the surgical repair for strength. If prostatic enlargement (whether due to cancer or benign prostatic hyperplasia) is present, castration is recommended. Additional surgery may be required depending on the individual circumstances.